An expanded molded article of styrene-modified olefin-based resin beads has been widely utilized as a goods-delivery box of mechanical parts such as an automobile part and the like, or a buffering packaging material of an electric product and the like, due to its excellent impact resistance, wear resistance and oil resistance.
However, since a styrene-modified olefin-based resin has high electric insulating property, the resin is easily electrified by friction, and appearance of an expanded molded article is deteriorated by dust attachment. In addition, since pollution or electrostatic breakage due to dust collection is caused in a content, there is a problem for using a packaging material of an electronic part as a liquid crystal display.
For the purpose of electrification prevention, there are known a method of covering surfaces of resin beads with an antistatic agent, and impregnating them with a blowing agent (Japanese Unexamined Patent Publication No. SHO 63(1988)-125537), a method of covering surfaces of expandable styrene-based resin beads with a particular antistatic agent (Japanese Examined Patent Publication No. SHO 59(1984)-35923), a method of covering surfaces of molding pre-expanded beads with an antistatic agent, and obtaining a molded article (Japanese Unexamined Patent Publication No. SHO 58(1983)-176227), and a method of modifying an olefin-based resin with a particular hydrophilic monomer, and making a surfactant contained therein (Japanese Unexamined Patent Publication No. HEI 10(1998)-147660).
However, in the aforementioned method of covering surfaces of resin beads with the antistatic agent, and impregnating them with the blowing agent as disclosed in Japanese Unexamined Patent Publication No. SHO 63(1988)425537, there is a problem that a dispersion system of the blowing agent at impregnation becomes unstable, so that binding of resin particles is easily caused.
In addition, in the aforementioned method of covering surfaces of expandable styrene-based resin beads with the particular antistatic agent as disclosed in Japanese Examined Patent Publication No. SHO 59(1984)-35923, there are problems that an addition amount of the antistatic agent for exerting antistatic property is increased, flowability of pre-expanded beads after completion of pre-expansion is deteriorated, and filling into an interior of a mold becomes insufficient at formation of an expanded article.
Further, in the aforementioned method of covering surfaces of molding pre-expanded beads with the antistatic agent, and obtaining the molded article as disclosed in Japanese Unexamined Patent Publication No. SHO 58(1983)-176227, there is a problem that the number of steps in a molding maker is increased.
Furthermore, in the aforementioned method of modifying the olefin-based resin with the particular hydrophilic monomer, and making the surfactant contained therein as disclosed in Japanese Unexamined Patent Publication No. HEI 10(1998)-147660, an expanded molded article which is excellent in antistatic property, and immediately exhibits electrostatic effect even by cracking, breakage or water washing can be obtained; however, there is a problem that since a polymerization rate of the hydrophilic monomer is worse and the monomer is expensive, a cost is increased.